Observational tests of world models

Abstract

Observational cosmologists owe a great debt to H. P. Robertson not only because his work clarified much of the confusion which surrounded the observational approach to the cosmological problem in the 1930’s but also because his rigorous derivation of the two fundamental equations which connect theory and observation (i.e. the metrical and apparent luminosity relations) established beyond doubt their validity. During his career, Robertson returned again and again to the problem, each time with new insight, and each time to clarify the observational approach. He, together with Heckmann and McVittie, were foremost in casting the theoretical equations exclusively in terms of observables such as redshift, apparent luminosity, and angular diameter, which can be determined at the telescope. The influence of Robertson on the observers was enormous. He took great interest in the new developments connected with the 200-inch project, and his council concerning theoretical interpretation of the observations was always given liberally. It is my privilege in this memorial symposium to retrace some of the logical development of the theory, to show how observational relations follow from Robertson’s methods in deriving the models, and finally to indicate where progress has been made in comparing the resulting predictions with the real world.